Surge diverter



Sept. 7, 1954 s. A. vR-rs ET AL SURGE DIVERTER Filed May 26, 1950 l 'abl /oo Invemor m o SS Png fri" WN en @JH a e d d n n e Ym, 5E d m a QWorm@ Y,

Patented Sept. 7, i954 SURGE DIVERTER Svend Aage Vrts and Erland BertilNilsson, assignors to Allmanna Svenska Elektriska Aktiebolaget,Vasteras, Sweden, a Swedish corporation Application May 26, 195o, serialNo. 164,355

Claims priority, application Sweden June 18, `1949 Ludvika, Sweden,

Modern surge diverters usually consist of a series of spark gaps inseries with a Valve resistor, usually consisting of blocks of a materialwith voltage dependent resistance. At high voltages, these parts havebeen enclosed in a series of tubular insulators. The number ofinsulators or units arranged above each other is determined by the linevoltage. As the spark gaps moreover are generally connected in parallelwith controlling resistors, an even voltage stress is obtained on thespark gaps at low steepness of the Wave front of the over-voltages, butat high steepness, the voltage distribution is determined by thecapacity conditions. This causes a lower ignition voltage on the wholeseries of spark gaps at high steepness than at a low one. By itself itis not inconvenient if the decrease of the ignition voltage only sets inat a considerably high steepness. If, however, the decrease of theignition Voltage sets in at a low steepness, it is possible that thesurge diverter is ignited at normally occurring switching over-voltages,which generally is not desirable.

By the uneven voltage distribution also the extinguishing ability of theWhole series of spark gaps is lowered as a consequence of the fact thatif a spark gap in the series is not capable of withstanding the recoveryvoltage, it re-ignites,` with the result that also the following lsparkgap ignites, and so on, until the whole series has ignited. Also by thisreason it is desirable that the even voltage distribution is maintainedup to considerably high steepness.

The present invention relates to a surge diverter, especially for highvoltages in which the above mentioned uneven voltage distribution isconsiderably equalised, and it is characterised in that the total numberof spark gaps in the diverter is distributed on the diierent units inapproximate proportion to the natural voltage distribution along thediverter, i. e. the voltage distribution which is caused by the capacityconditions. By this means, the Voltage stresses on all the spark gapswill be about the same.

The invention will be best understood with reference to the accompanyingdrawing, in which Figure 1 shows a section through the surge diverter,whereas Figure 2 shows a diagram of the voltage distribution.

In Figure 2, the dash-line curve shows the approximate voltagedistribution along a pile of insulators according to Figure 1, withoutprecautions for voltage equalisation, whereas the full-line curve showsthe voltage distribution along the insulators according to the arrange-3 Claims. (Cl. 317-70) ment shown in Figure l, and the chain-line curverepresents the voltage distribution inside the insulators, i. e. alongthe resistors and piles of spark gaps, before the diverter has ignited.

In the form of the invention shown in the drawing, l designates theinsulator cylinders piled on each other and held together by means ofmetal anges 2. A connecting terminal for the line is denoted 3, and 4 isa voltage equalising metal ring which by means of arms 5 is supported bythe top flange 2. Inside the insulators l, piles of spark gaps 6 arearranged, in series with which in every unit are arranged piles o'fvoltage dependent resistor blocks l. The bottom unit contains only suchvoltage dependent resistors.

Because of the fact that the insulators may become outwardly conductiveowing to dust or moist coating, it is possible to obtain a voltagedistribution across lthe different units, not corresponding to thenormal voltage distribution, and thus neither to the distribution of thespark gaps. This may cause an overstrain of the spark gaps in the unitswhich contain a smaller number of spark gaps. According to theinvention, this is prevented by adapting the effective external lengthof the insulators to the number of spark gaps' in the diverter units byoutwardly shortcircuiting part of them. In the form shown, this isobtained by providing the outside of the insulators at a suitable heightwith a bandage 8, conductingly connected with the anges 2 at the lowerpart of the insulators. This bandage may of course be substituted bymetallising or some other conducting covering.

It is not necessary that all units contain spark gaps, but in some casesit may be convenient to connect one or several units, only containingresistors, in series with units containing spark gaps.

We claim as our invention:

1. A surge diverter comprising a plurality of insulator cylinders piledupon each other, conducting anges joining said cylinders, voltagedependent resistors in said cylinders, and a number of series connectedcombined switching and quench spark gaps of equal length in eachcylinder in series with said resistors, said number being different ineach cylinder and accommodated to the voltage -falling on each cylinderdue to the natural capacitive voltage distribution atthe appearance of avoltage surge.

2. A surge diverter comprising a plurality of insulator cylinders piledupon each other, conducting fianges joining said cylinders, voltage dependent resistors in said cylinders, a number of pendent resistors insaid cylinders, a number: of.

series connected combined switching and. quench spark gaps of equallength in each cylinder in series with said resistors, sadiriumber being`diff ferent in each cylinder and accommodated to the voltage falling oneach cylinder due to the natural capacitive voltage distribution at theappearance ot a voltage surge,` and metallic. shields outside part ofthe cylinders each shield short-circuiting the external surface of thepart of the cylinder outside the resistors, said shields consisting of ametal bandage.

RefcrencesOltcd inrthmfile of this Apatent UNITED STATES PATENTS NumberName Date 1,754,158 Goodwin Apr. 8, 1930 2,032,566 Earle Mar. 3, 19362.1351135 Ludwig Nov. 1, 1938 2,179,297 Johnson Nov. 7, 1939 2;298,114fEitorff Oct. 6, 1942 2,586,285 Ackermann Feb. 19, 1952 FOREIGN PATENTSNumber Country Date 343,049 Great Britain Feb. 11, 1931 699,016Germany.- Nov. 21, 1940

